Forecast Intercomparisons from Three Numerical Weather Prediction Models

Abstract A forecast intercomparison study using six different initial states was carried out with forecasts made by the 2.5°, six-layer, second-generation National Center for Atmospheric Research (NCAR) general circulation model (GCM); the 4° × 5°, nine-layer Goddard Institute for Space Studies (GISS) GCM; and the 4° (at 50°N), six-layer National Meteorological Center (NMC) operational model. The initial conditions for geopotential and velocity were obtained from the NMC operational analyses during December 1972 and January 1973 for the Northern Hemisphere. The operational NMC analyses were used for verification of the forecast 1000 and 500 mb heights. Forecast projections to either three or five days were examined using conventional skill scores, wavenumber analysis of longitude-time plots constructed from the forecasts, and maps of the actual difference (forecast minus verification). The forecast errors were defined for each model and the common errors in all three forecasts were identified. The GISS an...